There has been known an electric power steering device which, in the case of abnormal stoppage, can specify whether a battery or a power feeder is a cause of failure. For example, in Patent Literature 1, an output voltage of a power source and a current flowing in a power feeder are detected by a battery sensor, and it is specified whether a battery or the power feeder is a cause of failure, based on the detected output voltage and the detected current flowing in the power feeder.
In Patent Literature 1, the battery sensor is provided outside an electronic control unit (ECU). Hence, the ECU needs to be provided with a terminal and a reception circuit for acquiring a detection value of the battery sensor. Further, since the battery sensor itself needs to be monitored, the device might be increased in size.
Patent Literature 1: Japanese Patent No. 5205981